Process to improve formulations of hydrocarbon conversion catalysts through removal and modification of detrimental particles and reuse of modified fractions

ABSTRACT

An improved hydrocarbon conversion catalyst is obtained through removal and modification by various means, of detrimental large and/or small particle fractions. Such modified fractions may be reused in the same or similar processes. The improved catalyst is advantageous to a wide range of hydrocarbon conversion processes.

CROSS REFERENCE

This application is a divisional filing of application Ser. No.13/422,013, filed Mar. 16, 2012, which in turn claimed priority to andthe benefit of priority to U.S. Provisional Application No. 61/465,390,filed on Mar. 19, 2011, the entirety of which is incorporated herein byreference.

TECHNICAL FIELD

Hydrocarbon conversion catalysts are improved through the removal ofparticles above a minimum size threshold and below a maximum sizethreshold, such that the increased average particle size results inimproved accessibility or diffusion in the conversion reactions.

BACKGROUND OF THE INVENTION

The present invention relates generally to hydrocarbon conversioncatalysts. Hydrocarbon conversion catalysts are materials that are usedto achieve a higher efficiency with respect to the yields and/or theselectivity of chemical reactions conducted to enhance the value ofhydrocarbons. An example of the use of such a catalyst is found in theFluid Catalytic Cracking (FCC) process in petroleum refineries, In theFCC process, a hydrocarbon feedstock with a boiling point usually higherthan 650° F. is reacted with a powdered catalyst to produce greaterquantities of higher value products that include gasoline, light cycleoil, heavy cycle oil, liquified petroleum gas and other light gases. Thecatalyst enhances the product yields when compared to a similar reactionwithout the presence of the catalyst.

The present invention is focused on hydrocarbon conversion catalystsknown in the Art as “fluid solid” catalysts and the materials used ascomponents in such catalysts. These catalysts are designed such thateven though the catalyst is a solid (solid particles) it behaves like aliquid when enough fluidizing media (e.g. vapors, air) are present. Ingeneral, the average particle size of a hydrocarbon conversion catalystparticle is between 60 and 90 microns. Two important parameters of suchcatalysts are the percent, by weight, of the total particles that have aparticle size below 20 microns and the percent by weight of the totalbelow 40 microns.

The first parameter (below 20 microns) is important as an indication oflosses or potential losses, as hydrocarbon conversion systems aregenerally designed with a cutoff in efficiency at around 20 microns, andparticles below 20 microns are more difficult to prevent from release tothe atmosphere and therefore more likely to present an environmentalproblem. The losses can be detrimental both economically andenvironmentally. Cyclonic systems or cyclones and air separators arewell known devices used in the Art to separate materials of differentphysical properties. In particular, cyclones can separate mixtures ofsolids with different particle size, density, relative mass or anycombination thereof. Particles below 20 microns are lost very rapidlyfrom the air cyclone process and either captured by higher efficiencysystems downstream or emitted to the atmosphere. The second parameter,the 0-40 micron content, is also significant, as particles in the 20-40micron range are important for fluidization in the hydrocarbonconversion system. Poor fluidization stemming from a relatively lowcomponent of smaller particles can result in reduced catalystcirculation or fluid bed instability.

The chemical nature of hydrocarbon conversion catalysts is well known tothose versed in the Art. These catalysts generally contain zeolite Y inone or several forms (RE-Y, USY, RE-USY, CREY, etc) as the main sourceof activity and selectivity. Some other mates like ZSM-5 can be added tochange the selectivities both as an intrinsic part of the catalyst or asa separate additive particle. Aluminas or silica aluminas of differentproperties are sometimes added to increase the activity of the catalystfor conversion of heavy molecules (bottoms upgrading). Clay is used as afiller that assists with the catalyst's chemical and physicalproperties. A binder, generally a low molecular weight oligomer ofsilica (Silica Sol), or aluminum chlohydrol (Alumina Sol) is commonlyadded to the mixture, which is spray dried to form the particles thatare shipped for usage, with or without a post-treatment step to adjustthe chemical composition and set the desired selectivities. Another typeof commercially available hydrocarbon conversion catalyst, the so called“In-Situ” technology, takes preformed spray-dried particles of Kaolinclay and other materials such as silica and aluminas and chemicallytreats them to form Zeolite Y based hydrocarbon conversion catalysts.

Solid hydrocarbon conversion catalysts are commonly made by spray dryingslurries that contain a mixture of the desired components that usuallyinclude, as discussed above, the zeolite Y, clay, alumina and a binderwhich can be based on silica sols, alumina sols or mixtures of both. Inone particular technology, a highly peptizable alumina itself becomesthe primary binder. In another technology, a particle containing claytreated at specific conditions is formed via spray drying and then isprocessed to grow zeolite Y. Other components such as silica or alumina,or both, can be added to the clay for specific properties.

Typically, the slurry is spray-dried to give a more or less sphericalshaped particle. The particle size distribution of the spray-driedmaterial is a function of the spray drier conditions and the nature andcomposition of the slurry. In general, the desired properties include:(1) a minimal amount of the 0-20 micron particles, (2) 10-20% of theparticles being between 20-40 microns, and (3) an average particle sizedistribution between 65 microns and 85 microns. In general, hydrocarbonconversion catalysts are made as a continuum of particle sizes andcompositions determined by the slurry properties and the spray drierconditions. In some cases, an air classifier is used to remove thesmaller particles to meet certain specifications. In general, the 0-40micron content can be controlled by the use of air classifiers, but thispractice is costly, as the efficiency of the classifiers is poor, andvaluable catalyst is commonly lost in this practice in order to meet aspecification.

The chemical reactions that occur in the hydrocarbon conversion processcan be diffusion limited. In general these reactions are defined asreactions in which mass transport of reactants into the catalystparticle limits the reaction efficiency. In commercial processes, manyreactions occur, and some may be diffusion limited, while others arenot. Another way to define such reactions is that the amount of reactionor the product yields are dependent on the particle size of the solidcatalyst. These conditions of “diffusion limitation” are also common tomany other catalytic processes. For example, nickel-containinghydrocarbons are very large, and react primarily on the outer-mostlayers of an FCC catalyst particle. This results in most of the nickelbeing deposited on the outside of the particle. An analysis of the totalexternal area of the particles as a function of the radius of theparticles shows that in such instances, the nickel will bepreferentially deposited on the smaller particles due to a largerexternal area per unit of volume. Among the important hydrocarbonconversion processes that can be diffusion limited, and therefore inwhich mass transfer is key, are the solid-liquid/solid-solid reactionssuch as those for Biomass conversion of wood or cellulosic material incontact with a solid catalyst particle. In addition, other reactions inwhich the contact time is very short tend to also fall in the definitionof diffusion limited reactions.

Just as nickel deposition on the hydrocarbon conversion catalystparticle is a function of particle size, many other reactions, somedesirable, some undesirable, are dependent on the particle size of thehydrocarbon conversion catalyst.

In general, the catalyst composition of a hydrocarbon conversioncatalyst is the same across particle sizes. When mixtures of additivesare included, these additives may have a slightly different particlesize distribution. However, it is a clear characteristic of hydrocarbonconversion catalysts and additives used to date, to have a continuous,smooth particle size distribution.

While interpreting the terms used to describe the present invention, itis important to consider the different techniques used to measure theparticle size distribution of hydrocarbon conversion catalysts. Whenreferring to particle size distribution, this discussion of the presentinvention refers to the actual physical size as measured by physicalmethods (like a screen) in which after minimizing agglomeration orattrition, fractions are measured by whether or not particles are ableto pass through the screen without major external forces, with theexception of gravity and vibratory motion. In the case of lightscattering methodologies, which are well-known to a person in the Art,the particle size distributions are continuous by mathematicalmanipulations of the experiments. Such continuum is an approximation andit is a limitation of the light scattering technique.

In general terms, the processes and resulting catalyst formulations ofthe present invention remove two major constraints, thereby enhancingthe value of solid hydrocarbon conversion catalysts. Large particles canbe detrimental to the processing of the largest molecules in a chemicalreaction where a short contact time is required to optimize thereaction. Large molecules cannot effectively transfer to and from theinside of the particle, and the total external surface area of largeparticles is substantially less than that of a similar amount ofcatalyst with a smaller particle size. However, removal of largeparticles results in the concentration of smaller particles. Thisconcentration of smaller particles can be beneficial if the initialcontent of particles below the minimum optimal threshold is below itsoptimum. However, a concentration of smaller particles can also bedetrimental, if there are too many fine catalyst particles and, as aresult, these particles are not properly retained by the hardware.Therefore, the catalyst composition may need to also have smallerparticles removed for optimal performance. When the value of thecatalyst is considerable, in order to enhance commercial viability, theremoved particles may need to be reused in another, or the same,process. Maximum recovery can be achieved if the removed large particlescan be reduced in size and if the removed smaller particles areconverted into larger particles by re-spray-drying.

Such improvements on the control of particle size are not known in theArt and have not been attempted before. The removal of fine particles byair classification to minimize losses of fine particles is known in theArt. However, unlike the present invention, such practice, which helpsto control physical losses from the process, results in catalyst with amuch larger concentration of large particles that is often detrimentalto the overall catalytic performance of the system. The use of theclassified fines as fluidization aids is also known in the Art. However,the process of the present invention that involves the removal andreprocessing of the larger particles of the catalyst system is not knownin the Art. On the contrary, although experts in the field acknowledgediffusion limitations, the leading work performed in the Art up to thistime has been done under the assumption that the major limitation is atthe molecular level, where the pore structure of the catalyst is thelimitation. The present invention clearly shows, contrary to thecommonly accepted viewpoint, that in many cases, the diffusionlimitation is a mass transfer phenomena to and from the catalystparticle. This diffusion limitation is at a micron scale, rather than atthe molecular scale commonly assumed in the Art. Molecularconsiderations imply diffusion limitations at a nanometer or angstromscale. The present invention clearly demonstrates a previously unknownand unsuspected improvement on yield structure. The focus of the currentArt has for decades been on improving a catalyst's pore structure,rather than the improvements on mass transfer phenomena at a much largerscale of the present invention.

SUMMARY OF THE INVENTION

The present invention provides for a method of making a spray-driedcatalyst composition for use in any hydrocarbon conversion process. Thismethod includes removing more than 50% of particles above and also morethan 50% of particles below a specified threshold and reprocessing theremoved particles to reduce particle size for use in the same or asimilar process. The spray-dried catalyst composition can be a freshcomposition, an equilibrium composition, or a combination of freshcatalyst and equilibrium catalyst.

The particles in the catalyst composition that are larger than thespecified threshold can be removed by any practical method, includingair classification or screening, or by a combination of airclassification and screening. The specified thresholds can be 110microns, 100 microns, 90 microns, 80 microns, 70 microns, 60 microns, 50microns, 40 microns, 30 microns, or 20 microns. The hydrocarbonconversion process can depend on particle size for reaction rate oryields.

The present invention also provides for a composite catalyst compositionfor use in any hydrocarbon conversion process that is dependent on theparticle size. The fraction of catalyst above the threshold can beprocessed by a milling media to reduce its particle size. Of particularusefulness are mills, or media mills, that allow for control of theresidence time or contact time between the milling media and thecatalyst. In a preferred embodiment of this invention, a dry media millcoupled with an air classifier is used to control the milling severityon the catalyst. Control of the severity is used to minimize theformation of particles below 20 microns. In another embodiment of thisinvention, the particles that are not used in the catalyst composition,specifically those below 20 microns, are re-formed into larger particlesvia any compounding/agglomeration technique like spray-drying, extrusionand other common agglomeration method known in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photographic representation of Fresh FCC Catalyst withoutmodification.

FIG. 2 is a photographic representation of Fresh FCC retained on a 95micron screen.

FIG. 3 is a photographic representation of Fresh FCC Catalyst passedthrough a 95 micron screen without smaller fines.

FIG. 4 is a photographic representation of the greater than 95 micronfraction after milling.

FIG. 5 is a photographic representation of the final FCC CatalystProduct after removal of fines by air classification.

FIG. 6 is a photographic representation of the fines generated by themilling step.

FIG. 7 is a graph showing test results conducted with an ACE unit.

DETAILED DESCRIPTION OF THE INVENTION

Numerous reactions in many industrial processes are dependent on theparticle size of the catalyst. Of particular importance forconsideration in the present invention are Fluid Catalytic Cracking(FCC), Deep Catalytic Cracking (DCC), BIOMASS Catalytic Conversion,Naptha Cracking to Olefins and other hydrocarbon conversion processes.State of the art catalyst manufacturing techniques for the catalystsused in such hydrocarbon conversion processes that are sensitive to theparticle size distribution, do not have a good control on the number oflarge particles that are formed. Typically, commercial fluid catalysts(commonly made in commercial spray driers) contain somewhere around20-40% of their weight in the particle size range above 100 microns.This high a percentage of such large particles is disadvantageous to theefficient operation of the process and is therefore not optimum forcatalyst composition.

It has been discovered that large catalyst particles are detrimental todiffusion limited reactions. The present invention solves this problemthis problem by providing a method to make catalysts with improvedperformance by removal of the particles above a defined threshold. Ithas also been shown that although fine particles in the 20-40 micronregime are desirable from a catalytic and fluidization perspective, manycommercial reactors do not retain these particles efficiently, and alarge percentage of these fine particles are lost from the process, andhave to be captured to avoid having such particles released to theenvironment. Furthermore, downstream units, such as power recoveryturbines, are very sensitive to the total amount of catalyst particlesimpacting them and can be adversely effected when impacted by fineparticles that are lost from the process.

When using fresh catalyst, it is not economically viable to reject20-40% of a product (i.e. the large particles discussed above). Thepresent invention solves this problem through reprocessing of the largeparticles that reduces the particle size with minimal losses. Theapplications of these catalyst compositions of the present inventioninclude any hydrocarbon processing that is sensitive to particle size.

The present invention has a very wide range of applicability. Thepresent invention is generally applicable to any and all hydrocarbonconversion processes that are sensitive to particle size, including, butnot limited to hydrocarbon conversion processes with catalysts having anoptimal average particle size between twenty (20) microns and onehundred (100) microns. These processes include, but are not limited to:Fluid Catalytic Cracking; BIOMASS conversion (especially those startingwith solid biomass ground into small particles); Naphtha Cracking tolight olefins and Polymerization reactions.

It has been further discovered in the present invention that thecatalyst composition may also require the smaller particles to beremoved for optimal performance. Particularly when the value of thecatalyst is high, in the present invention, to enhance commercialviability, the removed particles may be reused in another or the sameprocess. In the present invention, maximum recovery can be achieved ifthe removed large particles are reduced in size and the removed smallerparticles are converted into larger particles by re-spray-drying.

In a preferred embodiment, of the present invention, a typical fluidhydrocarbon conversion catalyst will be modified as follows:

-   -   a) removal of most of the particles above a maximum threshold        (usually between 80 and 105 microns) via a physical screening        process, air classification or a combination of both,    -   b) removal of most of the particles below a minimum threshold        (usually between 20 and 40 microns via a physical screening        process, air classification or a combination of both,    -   c) as part of the process, the removed large particles will be        reduced in particle size to improve diffusion characteristics        while controlling the generation of fines with a size below a        defined minimum threshold. The particle size reduction should be        a minimum of 10 microns but preferably larger than 30 microns in        average, while minimizing the production of fines below the        minimum threshold (usually between 20 and 40 microns).    -   d) as a further part of the process, most of the particles below        the minimum threshold resulting from the particle size reduction        process as well as those in the original catalyst will be        collected and sent for further milling to an average particle        size below 10 microns, preferably below 5 microns, where they        will be combined with suitable binders and other typical        catalytic components for spray-drying.    -   e) in addition, the milled particles considered suitable for the        same process as well as those from the spray-drying of the fines        collected may be blended with the original or other similar        catalysts for maximum recovery.        Of course, the above description is only one preferred        embodiment, and other preferred embodiments of the invention may        omit one or more of the process steps listed above.

In another embodiment, the starting material may not be the finishedcatalyst but instead, an intermediate material. Such would be the case,for example, for hydrocarbon processing catalysts made by the “In-Situ”methodology currently practiced by certain suppliers in the catalystindustry, particularly in Asia. In such a case, under the presentinvention, the size selection may be done on the microspheres prior tothe crystallization and finishing steps. In such a case, where usuallyinactive microspheres are blended with finished catalyst, it would be ofsignificant commercial value to maximize the content of active particlesabove the minimum threshold while the particles below the minimumthreshold could be inactive clay or a cheaper formulation, inclusive of,but not limited to, ECAT. The following examples demonstrate twoapplications of the present invention. These examples are illustrativeof the present invention, and the present invention is not limited inapplication to these examples

EXAMPLE 1 Fresh Catalyst

A fresh catalyst with a typical Particle Size Distribution (PSD) wasused as starting material (APS 68 microns), The coarser part of catalystwas then separated using a commercially available screener with a 95micron screen. This yielded about 35% of the original sample. Prior toscreening air classification of fines could be performed to speed up thescreening process.

The material retained on the screens was then fed and processed in amedia fluid mill containing 5 gallons of (1.8-2.7 mm in diameter)ceramic balls coupled with an air classifier. This system has the optionto re-circulate the milled product to control the severity or residencetime of the catalyst inside the mill. The higher the re-circulationrate, the slower the milling rate. In one preferred embodiment, theformation of particles smaller than 20 microns is minimized. FIG. 1shows the starting material prior to any separation.

EXAMPLE 2 Equilibrium Catalyst

An equilibrium catalyst was screened to remove the coarser fractionusing a 95 micron screen. This coarse fraction was then fed into the UFGmill filled with the ceramic media. The product was re-circulated atdifferent rates to change the severity of the milling step. The startingmaterial feed to the mill had an average particle size of 130 microns.

The Table below shows the results of the different experiments asmeasured by fines generation and average particle size. In order tochange the severity, the following parameters were changed:

-   -   RPM on the UFG mill changed from 150 to 250 rpm.    -   Feed rate from 84 lb/hr to 220 lb/hr.

Equilibrium catalyst Intial >95 μm Test 1 Test 2 Test 3 Test 4 Test 5Product APS, μm 79 130 114 102 40 68 85 73 <20 μm 0 0 0 1.5 25 8 5 2 <40μm 6 0 4 14 50 20 13 10 <95 μm 67 8 28 44 95 80 63 79Particle sizes in this table are measured by light scattering. Asdiscussed above, these experiments do not reflect the actual size in anabsolute manner. These experiments represent valid trends within thelimitations of this measurement technique.

As shown in FIG. 1, the starting point for modification by the presentinvention is a production run of catalyst. After the larger-than-95micron component is removed by screening, the large particles remain onthe screen, as shown in FIG. 2.

The less-than-95 micron component is shown in FIG. 3, after the smallerfines have been removed. After the larger-than-95 micron component ismilled the component takes on the appearance shown in FIG. 4.

The final product catalyst is shown in FIG. 5, after fines have beenremoved by air classification. Fines generated by the milling step areshown in FIG. 6.

FIG. 7 graphically describes the results of removing the larger-than-95micron particles from the standard FCC catalyst. Quanta represents thecompleted catalyst following the application of this one preferredembodiment of the present invention.

In accordance with the Patent Statutes, I have shown and described myinvention and claimed what I now consider to be its best embodiments.The invention may be practiced other than as described in thespecification so long as it is defined by the enclosed claims.

I claim:
 1. An improved Deep Catalytic Cracking process comprising thestep of subjecting a heavy hydrocarbon feedstock to an improved catalystcomposition, wherein the improved catalyst composition is prepared by aprocess comprising the steps of a. spray-drying a mixture comprising ahydrocarbon conversion catalyst to form solid hydrocarbon conversioncatalyst particles; removing greater than 50% of the particles below aminimum particle size threshold; and b. removing greater than 50% ofparticles above a maximum particle size threshold.
 2. An improvedBIOMASS conversion process comprising the step of subjecting a biomassto an improved catalyst composition, wherein the improved catalystcomposition is prepared by a process comprising the steps of a.spray-drying a mixture comprising a hydrocarbon conversion catalyst toform solid hydrocarbon conversion catalyst particles; removing greaterthan 50% of the particles below a minimum particle size threshold andgreater than 50% of particles above a maximum particle size threshold.3. An improved naphtha cracking process comprising the step ofsubjecting naphtha to an improved catalyst composition, wherein theimproved catalyst composition is prepared by a process comprising thesteps of a. spray-drying a mixture comprising a hydrocarbon conversioncatalyst to form solid hydrocarbon conversion catalyst particles;removing greater than 50% of the particles below a minimum particle sizethreshold and greater than 50% of particles above a maximum particlesize threshold.